1. Field of the Invention:
This invention relates to microwave devices, particularly to microwave filters and power limiters.
2. Description of the Prior Art:
In the prior art magnetic coupling between a YIG sphere and a transmission line to form a microwave filter or power limiter was accomplished by physically placing the YIG sphere in close proximity to the transmission line or between conductors of the transmission line. For example, for relatively light magnetic coupling, the YIG sphere may be placed between a straight transmission line and a ground plane. For large YIG spheres, the YIG sphere diameter may exceed the spacing between the transmission line and the ground plane. In such a case, additional space may be provided by forming a recess including a dimple for accepting the protrusion of the YIG sphere as described in U.S. Pat. No. 3,740,675 issued on June 19, 1973 and assigned to the assignee herein.
For tighter magnetic coupling, it has been common practice to form an arc or loop in the transmission line over the sphere with a ground plane below. The loop in the transmission line increases the inductance in the sphere region which helps to concentrate the radio frequency magnetic field. The loop in the transmission line, however, is very difficult to form and install over the YIG sphere at microwave frequencies such as X band because of its small size. The use of very small spheres within the range available increases the difficulty of installing the top conductor having a loop over the sphere.
It is therefore desirable to provide tight magnetic coupling between a transmission line and a YIG sphere, large or small, by a readily fabricated structure.
It is furthermore desirable to provide tight magnetic coupling between a transmission line and a plurality of YIG spheres by a readily fabricated structure.